$ F = \left[\begin{array}{rrr}1 & 0 & 4 \\ -2 & 2 & 4 \\ 2 & 1 & 1\end{array}\right]$ What are the dimensions of matrix $ F$ ?
Answer: The first dimension is the number of rows in the matrix. How many rows does $ F$ have? The second dimension is the number of columns in the matrix. How many columns does $ F$ have? So, $ F$ is a 3 $\times$ 3 matrix.